Hormone-refractory prostate cancer, the second leading cause of cancer death in US males, is noted by the aberrant and persistent expression of activated STAT3, a transcription factor whose activation is transient and under tight regulation in benign cells but not in malignant cells. Prostate cancer is the most diagnosed adeno-carcinoma in American men, with over 220,000 cases diagnosed in 2003 and over 232,000 predicted for 2005. Due at least in part to its intrinsic chemoresistant nature, prostate cancer is the second leading cause of cancer death for American men, accounting for over 30,000 deaths last year and predicted to cause at least that many this year. Recently physicians have documented that neither radical prostatectomy nor androgen-ablation therapy contributes to overall increased long-term survival. Therefore new treatments are urgently needed. New treatments are urgently needed. Malignant cells become dependent upon STAT3 for survival. Peptide nucleic acids (PNAs) are DNA mimics, wherein the phosphodiester backbones are replaced by neutrally-charged polyamines. PNAs are resistant to protease and nuclease degradation. They bind to duplex nucleic acids with high affinity, high enough to displace bound transcription factors. Thus PNAs complementary to STAT3 binding sites could serve as therapeutic agents for the treatment of prostate cancer. However because PNAs have poor cellular uptake they need further modification to enhance their therapeutic activity. One such modification is covalently-bound targeting vectors to enhance their uptake by the malignant cell. Previously 13410, an oligonucleotide we designed to inhibit STAT3 activity, induced apoptosis and slowed the growth of prostate cancer cell xenografts. Because PNAs offer advantages over oligonucleotides, they have become our major focus for anticancer agents. Preliminary data showed that one vector, TAT (trans-activator of transcription peptide of HIV), enhanced PNA uptake by prostate cancer cells, and that TAT coupled to a PNA having the sequence of 13410 induced apoptosis in prostate cancer cells. Studies are proposed with two specific aims. First, the PNA sequence and targeting vector will be optimized by testing several STAT3 binding sequences coupled to each of three candidate vectors. In vitro assays measuring intracellular localization, uptake kinetics (of fluorescently-labeled PNAs), apoptosis, cell proliferation, and effect on STAT3-regulated target genes will reveal the most effective combination of PNA sequence plus targeting vector. In vivo optimization will be accomplished using fluorescently-labeled PNAs in mice and checking for their accumulation in xenografts and other tissue. Efficacy studies in vivo will show the effects of single dose and multiple doses of the most potent PNA-vector. Second, the molecular pathway leading to apoptosis of prostate cells will be investigated, using electrophoretic mobility shift and chromatin immunoprecipitation assays to quantify decreased STAT3:DNA binding, reporter gene assays to demonstrate specificity for STAT3, and other reporter gene assays to demonstrate lack of effect on other STATs by the PNAs. Prostate cancer is second leading cause of cancer death among men in the US, with over 232,000 cases diagnosed in 2005. Conventional therapy has little effect on the outcome of hormone-refractory prostate cancer. Thus new approaches for hormone-refractory prostate cancer are urgently needed. In its 1998 report, the Prostate Cancer PRG stressed the importance of targeted therapies, especially gene and cellular targeted therapies. Research into these areas are still NCI priorities, as shown on page 7-17 of the 2004 Prostate Cancer PRG Report on the NCI website. For FY 2003-2008, the identification and validation of new therapeutic agents is one objective to answer the PRG's ongoing priorities regarding treatment of hormone- refractory prostate cancer. The research proposed in this application is highly relevant to answering the objectives of the NCI, precisely because it would help to create a novel therapeutic agent for the treatment of hormone-refractory prostate cancer based on gene and cellular targeted therapy. [unreadable] [unreadable] [unreadable]